Ohmic Heating & extraction processing

Ram Niwas Jhajhria15AG63R29

Presented by:

Contents IntroductionConcept and PrincipleHow is it different from conventional heating Suitable products for ohmic heatingAdvantages Inactivation of microorganisms by ohmic heatingDesign point Factors affecting ohmic heatingElectrodes UsedExtraction processing using ohmic heatingReferences

Ohmic heating Ohmic heating is an advanced thermal processing method wherein

the food material, which serves as an electrical resistor, is heated by passing electricity through it.

In the ohmic process two electrodes literally pass electric current through the food, where it flows on a continuous basis in a static column.

Electrical energy is dissipated into heat, which results in rapid and uniform heating.

The heating occurs in the form of internal energy generation within the material.

Ohmic heating• Joule heating, • electrical resistance heating,• direct electrical resistance heating,• electro heating, • electro conductive heating

Concept of Ohmic Heating

How is ohmic heating different fromconventional thermal processing?

• During conventional thermal processing for particulate foods, significant product quality damage may occur due to slow conduction and convection heat transfer.

• Ohmic heating volumetrically heats the entire mass of the food material, thus the resulting product is of far greater quality than its canned counterpart.

• It is possible to process large particulate foods (up to 1 inch).

• In ohmic heater cleaning requirements are comparatively less than those of traditional heat exchangers due to reduced product fouling on the food contact surface.

Products suitable for ohmicheating

Ohmic heating can be used for heating liquid foods containing large particulates, such as soups, stews, and fruit slices in syrups and sauces, and heat sensitive liquids.

The technology is useful for the treatment of protenacious

foods, which tend to denature and coagulate when thermally processed.

Juices can be treated to inactivate enzymes without affecting the flavor.

Other potential applications of ohmic heating include blanching, thawing, online detection of starch gelatinization, fermentation, peeling, dehydration, and extraction.

Advantages• Fast• More uniform heating• Higher temperature in particulates than liquid can be achieved,

which is impossible for conventional heating• Minimum mechanical damage• High energy efficiency• Ease of process control & reducing maintenance cost.

How does ohmic heating inactivatemicroorganisms?

• The principal mechanisms of microbial inactivation in ohmic heating are thermal in nature.

• A mild electroporation mechanism may occur during ohmic heating. The principal reason for the additional effect of ohmic treatment may be its low frequency (50 - 60 Hz),which allows cell walls to build up charges and form pores.

Electroporation

• Electroporation is the formation of holes in a cell membrane due to individual ion pressure, which cause change in permeability of cell membrane, due to the varying the electric field

• The low frequency used in ohmic heating (50-60Hz) allows cell wall to build up charges and form pores, which is not the case with high frequency methods such as microwave heating, where the electric field is reversed before sufficient charge buildup occurs at the cell walls.

Design points

Electrical conductivities of solid and liquid phases & their important coefficients

A close matching of conductivities would be highly desirable If σ (elec. conductivity) of solid phase is lower than the liquid

phase particle concentration Particle orientation important if particle aspect ratio are far from

unity For cubic and spherical particles the effects are negligible.

Design points

If all the particles are of low σ ,and particle conc. Is high, than the entire mixture heats slowly

Problem in regulating sufficient voltage to ensure heating Unlike conventional heating, particle size has relatively

minor effects on heating rates. Particles containing fat must be handled with care. Fat melts and separates from solid in the mixture.

Factors affecting ohmic heating

Electrical conductivityTwo phase systemBulk elect conductivity values and individual values must be

consideredFood materials electrical conductivity varies from 10 2 m S

to 10 3 m S/cm Shape and orientation of the particle Volumetric heat capacity Thermal conductivity and solid liquid heat transfer coefficient Heating rate

Electrodes used in ohmic heaters• Electrodes in ohmic heating can be regarded as a ‘junction’ between

a solid-state conductor (i.e. current feeder) and a liquid-state conductor (i.e. heating medium).

• play a vital role by conveying the current uniformly into the heating medium.

• Various materials used as electrodes in different ohmic heating studies and applications include

• platinized-titanium (Stirling, 1987; Tzedakis et al., 1999), • platinum (Tzedakis et al., 1999), titanium (Assiry, 1996),• carbon/graphite (Gatchell, 1935; Moses, 1938),• stainless steel (Assiry, 1996; Wu et al., 1998; Assiry et al.,

2003),• rhodium plated stainless steel (Palaniappn et al., 1991).

• During ohmic heating at low-frequency (50 - 60 Hz) alternating currents, it was reported that corrosion of electrodes and apparent (partial) electrolysis were often encountered with most of those electrodes.

Extraction Processing

Pre-treatment process in solvent extraction processing Extraction time is reduced Amount of extracted product is significantly increased.

Oil extraction from rice bran:

Rice variety – : Basmati riceSolvent – : n-hexaneVoltage- : 270 VConducting medium- : Sodium Chloride

(1M, 0.1M, 0.01M)

Procedure:

1. Ohmic heating chamber2. Thermometer3. Wattmeter4. Ammeter5. Variac6. Current source

Took 25g rice bran Add 150ml sodium chloride as a conducting material in three

different concentrations 1M, 0.1M, 0.01M in three different experiments

Switch on the power source and fixed the current value to heat the material

Power is controlled in throughout the process to control the current

During process the parameters i.e. temperature with time, current and power is noted

After ohmicaly heating, the rice bran samples were taken out from ohmic heating chamber and washed with fresh water to drain out the sodium chloride solution and then heated in hot air oven at 75 ° C for 5 min.

Then this pre treated rice bran is subjected to solvent extraction in soxhlet apparatus at 72ºC, and extract the oil.

Result and Discussions Twenty-five grams of rice bran was taken and oil extraction was conducted. The volume of n-Hexane used for the extraction was 200 ml. The quantity of rice bran oil extracted was 0.53 ml with an extraction time of 185 min (Without ohmic heating)

Ohmic heating was introduced as a pre treatment before solvent extraction then the time of extraction was 54min only and the yield of oil 0.8 ml

Extraction time reduced to approx 70-75%

Oil yield increased significantly

References:Marcos Camargo Knirsch, Carolina Alves dos Santos, António Augusto Martins de Oliveira Soares Vicente,Thereza Christina Vessoni Penna, Trends in Food Science & Technology-Ohmic heating, a review, 2012.

https://en.wikipedia.org/wiki/Joule_heating

https://www.youtube.com/watch?v=pPhvE5f-KwE

Gopu Raveendran Nair, V.R Divya, Liji Prasannan, V. Habeeba, M.V. Prince, G.S.V. Raghavan, Ohmic heating as a pre treatment in solvent extraction of rice bran, June 2012